Ink jet printer

1. An ink jet printer comprising: an ink chamber in which ink is filled; an ejection nozzle from which the ink said ink in chamber is ejected; a pressure generating means for loading pressure to the ink in said ink chamber; a plurality of ink ejecting means for ejecting the ink in said ink chamber from said ejection nozzle onto a receiving medium with pressure generated by said pressure generating means, and with a plurality of types of ink each having a different density of a same color stored therein; a control means for controlling said ink ejecting means so that a plurality of types of ink each having a different density are ejected with a desired dot diameter onto said receiving medium according to an input image signal and are ejected in a range of reflection density by superpositioning a plurality of types of ink having different densities on the same position, wherein a diameter of a dot formed with a first ink type is fixed to a value based on a minimum diameter of said ink, such that the diameter of the dot formed with the first ink type is the same diameter over the range of reflection density, and a diameter of a dot for another of said plurality types of ink is adjusted over the range of reflection density; a driving means for relatively moving said ink ejecting means to said receiving medium; and an administrating means for controlling said control means and said driving means so that said plurality of types of ink each having a different density will be ejected one above another onto a same specified position on said receiving medium with a desired dot diameter.

2. An ink jet printer according to claim 1; wherein said control means controls said plurality of ink ejecting means with pulse signals and controls a pulse width of the pulse signal.

3. An ink jet printer according to claim 1; wherein said pressure generating means is a piezoelectric element, and said control means controls a rise time of a control signal for controlling said ink ejecting means.

4. An ink jet printer according to claim 1; further comprising a gradation converting means having a function to process a digital halftoning.

5. An ink jet printer according to claim 4; wherein said gradation converting means detects pixels included in a low density area and subjects the pixels included in the detected low density area to the digital halftoning processing.

6. An ink jet printer according to claim 4; further comprising an image distinguishing means for differentiating characters and illustrations from natural pictures based on input image signals; wherein said gradation converting means has a plurality of dither matrixes each having a different matrix size or a pattern array respectively and executes a dither processing using a different dither matrix for characters/illustrations and natural pictures respectively.

7. An ink jet printer comprising: an ink chamber in which ink is filled; an ejection nozzle from which the ink in said ink chamber is ejected; a pressure generating means for loading pressure to the ink in said ink chamber; an ink ejecting means for ejecting the ink in said ink chamber from said ejection nozzle onto a receiving medium with pressure generated by said pressure generating means and with a plurality of types of ink, each having a different density of a same color stored therein; a control means for controlling said ink ejecting means so that a plurality of types of ink each having a different density are ejected with a desired dot diameter onto said receiving medium according to an input image signal, and are ejected in a range of reflection density by superpositioning a plurality of types of ink having different densities on the same position, wherein a diameter of a dot formed with a first ink type is fixed to a value based on a minimum diameter of said ink, such that the diameter of the dot formed with the first ink type is the same diameter over the range of reflection density, and a diameter of a dot for another of said plurality types of ink is adjusted over the range of reflection density of a receiving medium to have continuous tone characteristics in the range of reflection density; a driving means for relatively moving and said ink ejecting means to said receiving medium; an administrating means for controlling and said control means and said driving means so that said plurality of types of ink each having a different density will be ejected one above another, each of said plurality of types of ejected ink having a desired dot diameter at a same specified position on said receiving medium; an image distinguishing means for differentiating characters and illustrations from natural pictures according to said input image signal; and dither processing means having a plurality of dither matrices each having a different matrix size or pattern array and executing a dither processing using a different dither matrix for characters/illustrations and natural pictures respectively.

8. An ink jet printer according to claim 7; wherein said ink ejecting means comprises a plurality of ink ejecting means with a plurality type of ink each having a same density.

9. An ink jet printer comprising: an ink chamber in which ink is filled; an ejection nozzle from which the ink in said ink chamber is ejected; a pressure generating means for loading pressure to the ink in said ink chamber; an ink ejecting means for ejecting the ink in said ink chamber from said ejection nozzle onto a receiving medium with pressure generated by said pressure generating means; control means for controlling said ink ejecting means so that said ink is ejected with a desired dot diameter onto said receiving medium according to an input image signal; a driving means for relatively moving said ink ejecting means to said receiving medium; an administrating means for controlling said control means and said driving means so that said ink will be ejected one above another with a desired dot diameter at a same specified position on said receiving medium; and a gradation converting means for detecting pixels included in a low density area according to said input image signal and subjecting the detected pixels in the low density area to digital halftoning processing, wherein said low density area is discriminated by a threshold value of density defined by the ink of lowest density with a minimum dot diameter, and said digital halftoning processing converts the pixels below the threshold value of density into processed data using threshold matrices to accomplish representing said low density area.

10. An ink jet printer according to claim 9 further comprising a plurality of ink chambers filled with ink, each ink having a same density.

11. An ink jet printer comprising; an ink chamber in which ink is filled; an ejection nozzle from which the ink in said ink chamber is ejected; a pressure generator for loading pressure to the ink in said ink chamber; a plurality of ink ejectors for ejecting the ink in said ink chamber from said ejection nozzle onto a receiving medium with pressure generated by said pressure generator, and with a plurality of types of ink each having a different density of a same color stored therein; a controller for controlling said ink ejector so that a plurality of types of ink each having a different density are ejected with a desired dot diameter onto said receiving medium according to an input image signal and are ejected in a range of reflection density by superpositioning a plurality of types of ink having different densities on the same position, wherein a diameter of a dot formed with a first ink type is fixed to a value based on a minimum diameter of said ink, such that the diameter of the dot formed with the first ink type is the same diameter over the range of reflection density, and a diameter of a dot for another of said plurality types of ink is adjusted over the range of reflection density of a receiving medium to have continuous tone characteristics in the range of reflection density; a driver for relatively moving said ink ejector to said receiving medium; and an administrator for controlling said controller and said driver so that said plurality of types of ink each having a different density will be ejected one above another onto a same specified position on said receiving medium with a desired dot diameter.

12. An ink jet printer according to claim 11, wherein said controller controls said plurality of ink ejectors with pulse signals and controls a pulse width of the pulse signal.

13. An ink jet printer according to claim 11, wherein said pressure generator is a piezoelectric element, and said controller controls a rise time of a control signal for controlling said plurality of ink ejectors.

14. An ink jet printer according to claim 11, further comprising a gradation convertor having a function to process a digital halftoning.

15. An ink jet printer according to claim 11, wherein said gradation convertor detects pixels included in a low density area and subjects the pixels included in the detected low density area to the digital halftoning processing.

16. An ink jet printer according to claim 14, further comprising an image distinguishing circuit for differentiating characters and illustrations from natural pictures based on input image signals; wherein said gradation convertor has a plurality of dither matrixes each having a different matrix size or a pattern array respectively and executes a dither processing using a different dither matrix for characters/illustrations and natural pictures respectively.